tests/test-empty.t

test-setdiscovery: make test compatible with chg

The test checks the output of the blackbox extension which will
contain logs corresponding to chg in case chg is running. Therefore, this
commit modifies the test to take chg into consideration while working with the
blackbox extension.

Test Plan:
Ran the test 'test-setdiscovery.t' with and without the '--chg'
option.

Differential Revision: https://phab.mercurial-scm.org/D926

Create an empty repo:

  $ hg init a
  $ cd a

Try some commands:

  $ hg log
  $ hg grep wah
  [1]
  $ hg manifest
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  0 files, 0 changesets, 0 total revisions

Check the basic files created:

  $ ls .hg
  00changelog.i
  requires
  store

Should be empty:

  $ ls .hg/store

Poke at a clone:

  $ cd ..
  $ hg clone a b
  updating to branch default
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd b
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  0 files, 0 changesets, 0 total revisions
  $ ls .hg
  00changelog.i
  hgrc
  requires
  store

Should be empty:

  $ ls .hg/store

  $ cd ..